US20020157541A1 - Temperature probe controller circuit - Google Patents
Temperature probe controller circuit Download PDFInfo
- Publication number
- US20020157541A1 US20020157541A1 US10/032,340 US3234001A US2002157541A1 US 20020157541 A1 US20020157541 A1 US 20020157541A1 US 3234001 A US3234001 A US 3234001A US 2002157541 A1 US2002157541 A1 US 2002157541A1
- Authority
- US
- United States
- Prior art keywords
- relay
- current
- solid state
- control signals
- state switch
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Images
Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B1/00—Details of electric heating devices
- H05B1/02—Automatic switching arrangements specially adapted to apparatus ; Control of heating devices
- H05B1/0227—Applications
- H05B1/0252—Domestic applications
- H05B1/0258—For cooking
- H05B1/0269—For heating of fluids
-
- A—HUMAN NECESSITIES
- A47—FURNITURE; DOMESTIC ARTICLES OR APPLIANCES; COFFEE MILLS; SPICE MILLS; SUCTION CLEANERS IN GENERAL
- A47J—KITCHEN EQUIPMENT; COFFEE MILLS; SPICE MILLS; APPARATUS FOR MAKING BEVERAGES
- A47J36/00—Parts, details or accessories of cooking-vessels
- A47J36/32—Time-controlled igniting mechanisms or alarm devices
-
- A—HUMAN NECESSITIES
- A47—FURNITURE; DOMESTIC ARTICLES OR APPLIANCES; COFFEE MILLS; SPICE MILLS; SUCTION CLEANERS IN GENERAL
- A47J—KITCHEN EQUIPMENT; COFFEE MILLS; SPICE MILLS; APPARATUS FOR MAKING BEVERAGES
- A47J37/00—Baking; Roasting; Grilling; Frying
- A47J37/10—Frying pans, e.g. frying pans with integrated lids or basting devices
- A47J37/105—Frying pans, e.g. frying pans with integrated lids or basting devices electrically heated
Abstract
A circuit for controlling the flow of electric current through a resistive element, the circuit including a relay and a solid state switch, and a microprocessor for generating control signals to direct current through the solid state switch when the magnitude of the current changes rapidly, and through the relay when the magnitude of the current is relatively stable.
Description
- This invention relates to the temperature control of heating appliances, in particular cooking appliances.
- Electric cooking appliances, such as electric pans and woks, allow the temperature of the appliance to be carefully controlled. This is often useful when cooking food which required precise cooking temperatures to optimise the flavour and texture of the food.
- Furthermore, the use of an electric cooking appliance provides for automated control of the cooking process, in that a cooking cycle may, in some cases, be programmed to increase and decrease the cooking temperature of the appliance at preset times. This leaves the cook or chef with more time to attend to other tasks.
- The circuits used to control the temperature of the appliance involve the provision of current to a resistive element, which dissipates the energy provided as heat. The level of energy, and thus heat dissipated, is proportional to the average power delivered via the current into the resistive element. Accordingly, controlling the amount of current being delivered to the resistive element will allow for the control of heat energy being dissipated by the resistive element.
- This is accomplished by “connecting and disconnecting” the load, or resistive element, to and from the current source. The ratio of the “connected time” to the “disconnected time” will determine the average power delivered to the resistive element, and accordingly determine the heat generated therefrom.
- This connection and disconnection is accomplished via an electronic switch, typically a relay. A relay is a mechanical switch which is actuated via electromagnetic means, causing a conductive element to switch from one position to another, as is well understood by those skilled in the art.
- Precise regulation of the temperature (amount of heat dissipated by the resistive element) requires that the switch be able to switch quickly and frequently. A problem with relays is that, being partly mechanical in nature, they have a limited life span, in that the number of times the conductive element is able to be switched before failing is limited.
- Ideally, more robust switching devices would be useful in this application. Solid state switches, such as triacs, adapt themselves well to fast switching. Such devices are also well known in the art. Triacs are able to switch between one conducting state and another extremely quickly and are far more long lasting in terms of the number of “switches” that can be performed in a lifetime. However, a serious disadvantage of such solid state switches is that they themselves dissipate a significant amount of power in the form of heat, and require the use of substantial heat sinks. This is a disadvantage, particularly in the application of kitchen appliances where space is often at a premium in such appliances and heat sinks can take up valuable space. Accordingly, such devices are not generally suitable in these applications.
- It is accordingly an object of the present invention to provide a temperature control circuit which is able to reduce space requirements while maintaining a longer product lifetime.
- According to a first aspect of the present invention, there is provided a control circuit for controlling the flow of current from a current source through a resistive element, the circuit including;
- a microprocessor for generating control signals;
- a relay for selectively connecting a current source to the resistive element in accordance with the control signals generated by the microprocessor; and
- a solid state switch for selectively connecting the current source to the resistive element in accordance with the control signals generated by the microprocessor, the control signals being generated to coordinate the switching of the relay and triac in order to reach and/or maintain a desired temperature.
- Preferably, the circuit is a temperature control circuit for a heating appliance.
- Preferably, the solid state switch is a triac.
- According to a second aspect of the present invention, there is provided a control circuit for controlling the flow of current from a current source through a resistive element, the circuit including;
- a solid state switch;
- a relay;
- a first comparator associated with said solid state switch and having a first threshold; and
- a second comparator associated with said relay and having a second threshold, wherein a control signal is applied to an input of said circuit causing said solid state switch to turn on when the magnitude of the voltage of said control signal exceeds said first threshold and wherein the relay is in an open state when said voltage magnitude is below said first threshold and in a closed state when the magnitude of said voltage is above said second threshold.
- According to a third aspect of the present invention, there is provided a method of controlling the flow of current through a resistive element, the method including the steps of;
- generating control signals;
- providing the control signals generated to a relay for selectively connecting a current source to the resistive element in accordance with the control signals; and
- providing the control signals generated to a solid state switch for selectively connecting the resistive element to the current source in accordance with the control signals, the control signals being generated to coordinate the switching of the relay and solid state switch in order to reach and/or maintain a desired temperature.
- A preferred embodiment of the present invention will now be described with reference to the following drawings.
- FIG. 1 shows a control circuit in accordance with a first embodiment of the present invention.
- FIG. 2 shows wave form timing diagrams for the first embodiment;
- FIG. 3 shows a system block control diagram for the first embodiment;
- FIG. 4 shows an output flow diagram for the first embodiment;
- FIG. 5 shows wave form timing diagrams for a second embodiment of the present invention; and
- FIG. 6 shows a control circuit for the second embodiment.
- Referring to FIG. 1, it can be seen that
resistive element 1 is connected between voltage source 2 and ground, or neutral point, 3. When so connected, a current i will flow throughelement 1. Voltage source 2 is an AC source, which causes AC current i to flow throughresistive element 1. As current i flows throughelement 1, energy is dissipated fromelement 1 in the form of heat. This heat is proportional to the power which is dissipated viaelement 1. This power is delivered toelement 1 via the current i and is proportional to the average power of that current signal. For sinusoidal current i, having a RMS current of IRMSamps, the average power P dissipated through the resistive element having a resistance of R ohms, is given by the well known relation - P=I2 RMS R
- Thus, the average power in the form of heat, generated by
resistive element 1 can be controlled by varying the average EMS current being delivered toelement 1. - Current i is allowed to flow through
element 1 when the path from source 2 toground point 3 is closed. The circuit 10 provides two paths for the current i to flow. Current i will flow through path 12 when triac 4 is on. Whenrelay 5 is actuated to form a short circuit in path 13, current i will flow through path 13. - When current i flows through path12, and accordingly through triac 4, a significant amount of heat is generated by triac 4. If the magnitude of the current is great, a substantially large heat sink will be required. If current i is in the order of 10 amps, the required heat sink will need to be able to dissipate about 12 watts. Such a requirement would normally make the use of a triac in this application unsuitable. However, in accordance with the present invention, the path taken by current i is alternated between path 12 through triac 4 and path 13 through
relay 5. In some cases, however, both the triac 4 and therelay 5 may be on at the same time, providing two current paths, even if only momentarily, as will be described in more detail further below. - In contrast,
relay 5 does not dissipate an appreciable amount of heat, regardless of the magnitude of current flowing through its conductive element 5a. - To optimise the working of the circuit10, microcontroller 8 calculates and generates control signals to open triac 4 and
close relay 5 such that current i flows through path 13 for current flows of long duration. Triac 4 however is used to take the load current momentarily to avoid contact splash, thus enhancing the relay life. Accordingly, in these instances, Micro-controller 8 generates signals to close triac 4 andopen relay 5, causing current i to flow through path 12. In instances where more rapid switching is required, again, triac 4 is used in preference torelay 5. In this way, large average RMS currents having greater average power will go through path 13 viarelay 5 which does not dissipate appreciable amounts of heat, while instances requiring fast switching and lower current power will make use of triac 4. Tis way,relay 5 is spared from having to switch on and off quickly and a greater number of times, while at the same time, the power dissipated by triac 4 will be reduced because only low powered current will flow therethrough. Accordingly, any heat sinks required by triac 4 will be far smaller than otherwise required. - To actuate
relay 5, micro-controller 8 will generate a signal to cause transistor 7 to conduct, by applying a voltage at the base of transistor 7 through resistor 14. Diode 6 provides a typical protection against the emf currents generated by the coil ofrelay 5. To switch triac 4 on and off, micro-controller 8 will generate a control signal to triac driver 11, which will actuate triac 4. - Exemplary timing and wave form diagrams illustrating the above are shown in FIG. 2.
- The input to micro-controller8 is provided by thermistor 9 which will provide a signal proportional to temperature sensed by thermistor 9. This analogue signal is converted to a digital signal by A/D converter 10 for input to micro-controller 8.
- The control signals generated by microcontrollers are generated in accordance with a control algorithm, which uses PIE) control principles to effectively maintain a desired temperature of the appliance.
- For example, if thermistor9 detects a sudden drop in the temperature of the appliance (which may happen if food is added to the pan for example), micro-controller 8 will generate signals to coordinate the switching of
relay 5 and triac 4 to immediately provide a high current surge throughelement 1, creating additional heat. This works in a predictive manner in that upon detecting a sudden temperature drop, micro-controller predicts the further reduction of temperature from the rate of the initial fall, and generates the appropriate control signals to compensate. This allows for fast and dynamic temperature regulation. - Turning now to FIG. 3, there is shown a block diagram of the control system used to calculate and generate control signals for the triac4 and
relay 5. The PID transfer function is again by: - U(s)=K p(1+1/T 1 s+T D s)E(s)
- The transfer function is a Laplace transform of the standard differential equations representing the PID equation, where:
- U(s) is the control output calculated by the PID transfer function.
- E(s) is the error input to the transfer function, which is usually a difference of the sensed parameter with respect to the desired set point
- Kp is the Proportional Gain
- TI is the Integral time
- TD is the Derivative time.
- Kp, TI and TD are adjusted to provide the desired response of the controller as is well understood in the art.
- FIG. 4 shows the output flow which represents the algorithm used to convert the output of the PID transfer U(s) to the control signals for the triac4 and
relay 5. The decision block “U(s)<Threshold” provides a simple mechanism for selecting between therelay 5 and triac 4 outputs, which controls the average power throughelement 1. The output frequency is also increased with triac activation. - While perhaps not as effective as the embodiment described above, it is also possible to control the operation of the
relay 5 and the triac 4 together rather than independently. - In this embodiment, (see circuit in FIG. 6) the triac4 is caused to switch on just before the relay contact 5 a closes, and is turned off just after relay contact 5 a opens. In this way, the relay contact 5 a is not stressed because it does not have current passing through it at times when the magnitude of the current changes rapidly. As discussed previously, fast switching causes excessive bouncing of contact 5 a and can cause contact arcing which may weld the contact 5 a to the
relay 5. - As shown in FIG. 6, the triac4 and
relay 5 are connected in parallel. A first comparator (comp 1) drives triac 4, while a second comparator (comp 2) drivesrelay 5. A signal is input to the on/off input which can be either analog or pulse width modulated. If the voltage at this signal does not rise above the threshold of comparator 1 (as set by R3/R1, R4) only triac 4 will turn on. If the voltage rises above a second threshold (as set by R4/R1, R3) then the relay will switch on. The result is that if therelay 5 does switch on, it will always do so after triac 4 switches on. - Thus at the times of fast changing current magnitude, triac4 comes on first and then at a time ΔT later, relay contact 5 a closes to provide an additional path for the current i, thereby bypassing the current away from the triac and through the relay contacts. Since the voltage across the relay contacts is lower than that across the triac, the triac will turn off, thus returning the triac to a zero power dissipation condition. When a reduction in load power is required (as sensed by the temperature sensor) the relay contacts will open, enabling current to be bypassed back through the triac for a short time. The triac is then either turned off or pulsed on and off at a low duty cycle without the relay contacts engaging, as long as the average power dissipated by the triac is well below its dissipation limit.
- The triac thus enables a low switching voltage across the contacts by current transfer, and allows the load current to be pulsed for a short time at high rates without relay operation.
- The timing diagram for this is shown in FIG. 5. There is a delay of ΔT after the triac switches on for relay closure and a delay of ΔT2 for the triac to turn off after the relay contacts open. ΔT2 is biased by usual triac action and cannot turn off until the current passing through the triac goes to zero, ie for a 50Hz sinusoid at the zero crossing point.
- It will be appreciated that the above has been described with reference to a particular embodiment and that many variations and modifications may be made within the scope of the present invention.
Claims (9)
1. A control circuit for controlling the flow of current from the current source through a resistive element, the circuit including:
a microprocessor for generating control signals;
a relay for selectively connecting a current source to the resistive element in accordance with the control signals generated by the microprocessor; and
a solid state switch for selectively connecting the current source to the resistive element in accordance with the control signals generated by the microprocessor, the control signals being generated to coordinate the switching of the relay and triac in order to reach and/or maintain a desired temperature.
2. A control circuit according to claim 1 wherein the control signals cause the relay and solid state switch to coordinate such that said current passes through said solid state switch when the magnitude of said current changes rapidly, and passes through said relay when the magnitude of said current is relatively constant.
3. A circuit according to any one of claims 1 or 2 wherein said solid state switch is a triac.
4. A circuit according to any one of claims 1 to 3 wherein said circuit is a temperature control circuit for a heating appliance.
5. A control circuit for controlling the flow of current from a current source through a resistive element, the circuit including;
a solid state switch;
a relay;
a first comparator associated with said solid state switch and having a first threshold; and
a second comparator associated with said relay and having a second threshold, wherein a control signal is applied to an input of said circuit causing said solid state switch to turn on when the magnitude of the voltage of said control signal exceeds said first threshold and wherein the relay is in an open state when said voltage magnitude is below said first threshold and in a closed state when the magnitude of said voltage is above said second threshold.
6. A circuit according to claim 5 wherein said solid state switch is a triac.
7. A method of controlling the flow of current through a resistive element, the method including the steps of;
generating control signals;
providing the control signals generated to a relay for selectively connecting a current source to the resistive element in accordance with the control signals; and
providing the control signals generated to a solid state switch for selectively connecting the resistive element to the current source in accordance with the control signals, the control signals being generated to coordinate the switching of the relay and solid state switch in order to reach and/or maintain a desired temperature.
8. A method according to claim 7 wherein said control signals cause the relay and solid state switch to coordinate such that said current passes through said solid state switch when the magnitude of said current changes rapidly, and to pass through said relay when the magnitude of said current is relatively constant.
9. A method according to any one of claims 7 or 8 wherein said solid state switch is a triac.
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AUPR2273A AUPR227300A0 (en) | 2000-12-22 | 2000-12-22 | Temperature probe controller circuit |
AUPR2273 | 2000-12-22 | ||
AU97318/01A AU9731801A (en) | 2000-12-22 | 2001-12-19 | Temperature probe controller circuit |
US10/171,517 US20030231695A1 (en) | 2000-12-22 | 2002-06-13 | Electrical plug display arrangement |
Publications (1)
Publication Number | Publication Date |
---|---|
US20020157541A1 true US20020157541A1 (en) | 2002-10-31 |
Family
ID=32180061
Family Applications (2)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US10/032,340 Abandoned US20020157541A1 (en) | 2000-12-22 | 2001-12-21 | Temperature probe controller circuit |
US10/171,517 Abandoned US20030231695A1 (en) | 2000-12-22 | 2002-06-13 | Electrical plug display arrangement |
Family Applications After (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US10/171,517 Abandoned US20030231695A1 (en) | 2000-12-22 | 2002-06-13 | Electrical plug display arrangement |
Country Status (4)
Country | Link |
---|---|
US (2) | US20020157541A1 (en) |
AU (2) | AUPR227300A0 (en) |
GB (1) | GB2378061A (en) |
NZ (1) | NZ516284A (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN108514343A (en) * | 2018-06-20 | 2018-09-11 | 佛山市艾美皓电子科技有限公司 | Double protection temperature control circuits and air fryer |
US10088169B2 (en) | 2016-07-15 | 2018-10-02 | Haier Us Appliance Solutions, Inc. | Cooktop appliance and method of operation |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6893153B2 (en) * | 2002-06-28 | 2005-05-17 | Hewlett-Packard Development Company, L.P. | Temperature-indicating power adapter and electronic device that operates therewith |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4638147A (en) * | 1983-10-18 | 1987-01-20 | Anthony Dytch | Microprocessor controlled through-flow electric water heater |
US5105067A (en) * | 1989-09-08 | 1992-04-14 | Environwear, Inc. | Electronic control system and method for cold weather garment |
US5866880A (en) * | 1995-10-10 | 1999-02-02 | David Seitz | Fluid heater with improved heating elements controller |
US6006996A (en) * | 1997-10-16 | 1999-12-28 | Varma Trafig Limited | Electronic thermostat control unit and its use in multipoint temperature controller for refrigeration and heating systems |
Family Cites Families (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE3425831A1 (en) * | 1984-07-13 | 1986-01-16 | Janke & Kunkel Gmbh & Co Kg Ika-Werk, 7813 Staufen | Heating device |
DE3622093C1 (en) * | 1986-06-27 | 1987-11-19 | Sachs Ersa Kg | Switch arrangement for supplying a load with alternating current |
GB2222278A (en) * | 1988-08-02 | 1990-02-28 | Turnright Controls | Control of electric heating |
DE29701352U1 (en) * | 1997-01-29 | 1997-04-17 | Domotec Ag | Circuit arrangement for switching an electrical alternating current flowing through a load on and off |
DE19808878B4 (en) * | 1998-03-03 | 2004-09-30 | Ifm Electronic Gmbh | Measuring device for process measurement technology |
-
2000
- 2000-12-22 AU AUPR2273A patent/AUPR227300A0/en not_active Abandoned
-
2001
- 2001-12-19 AU AU97318/01A patent/AU9731801A/en not_active Abandoned
- 2001-12-19 NZ NZ516284A patent/NZ516284A/en unknown
- 2001-12-20 GB GB0130394A patent/GB2378061A/en not_active Withdrawn
- 2001-12-21 US US10/032,340 patent/US20020157541A1/en not_active Abandoned
-
2002
- 2002-06-13 US US10/171,517 patent/US20030231695A1/en not_active Abandoned
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4638147A (en) * | 1983-10-18 | 1987-01-20 | Anthony Dytch | Microprocessor controlled through-flow electric water heater |
US5105067A (en) * | 1989-09-08 | 1992-04-14 | Environwear, Inc. | Electronic control system and method for cold weather garment |
US5866880A (en) * | 1995-10-10 | 1999-02-02 | David Seitz | Fluid heater with improved heating elements controller |
US6006996A (en) * | 1997-10-16 | 1999-12-28 | Varma Trafig Limited | Electronic thermostat control unit and its use in multipoint temperature controller for refrigeration and heating systems |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US10088169B2 (en) | 2016-07-15 | 2018-10-02 | Haier Us Appliance Solutions, Inc. | Cooktop appliance and method of operation |
CN108514343A (en) * | 2018-06-20 | 2018-09-11 | 佛山市艾美皓电子科技有限公司 | Double protection temperature control circuits and air fryer |
Also Published As
Publication number | Publication date |
---|---|
AUPR227300A0 (en) | 2001-01-25 |
AU9731801A (en) | 2002-11-28 |
GB0130394D0 (en) | 2002-02-06 |
GB2378061A (en) | 2003-01-29 |
US20030231695A1 (en) | 2003-12-18 |
NZ516284A (en) | 2002-10-25 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US4316080A (en) | Temperature control devices | |
EP2014140B1 (en) | Load control device having a variable drive circuit | |
US5894396A (en) | Inrush current protection circuit | |
US20080129124A1 (en) | Hybrid electrical switching device | |
JPS63277468A (en) | Power control circuit with phase-controlled signal input | |
EP3054746B1 (en) | Control apparatus using variations in conduction angle as control command | |
CA1337213C (en) | Dual bimetal power control switching arrangement for electronically controlled appliances | |
KR102154635B1 (en) | Coil drive appatatus | |
CN114080861A (en) | Load control device with closed-loop gate drive circuit | |
US20060290306A1 (en) | Electrical circuit arrangement for a power tool | |
JPS59158415A (en) | Heat efficiency adjusting circuit for heating element | |
US20020157541A1 (en) | Temperature probe controller circuit | |
US10816216B2 (en) | Method and apparatus for preventing cooktop fires | |
WO1995019659A1 (en) | A switching circuit | |
US6365988B1 (en) | Power controller for setting the power of the electrical loads of an electrical appliance | |
GB2294166A (en) | AC electric power switching arrangement; avoiding inrush currents in inductive loads | |
KR19980086732A (en) | Method and device for controlling the output of electrical consumption connected to ac line voltage | |
JPH09163593A (en) | Inrush current suppression circuit | |
KR102153498B1 (en) | Heating device for preventing over current | |
KR102175642B1 (en) | Heating device for preventing over current | |
GB2297439A (en) | Overload protection for phase-angle power controller | |
US5390071A (en) | Low interference controlled switching circuit for multiple loads | |
JP2008537460A (en) | Control circuit with low bypass switch load | |
CN115494894B (en) | Temperature control method of electric heating assembly | |
AU2009227973A1 (en) | Controlled switching |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
AS | Assignment |
Owner name: MISTRAL INTERNATIONAL PTY LTD., AUSTRALIA Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:CHEAH, PIN;RICHARDS, DAVID;REEL/FRAME:012981/0337 Effective date: 20011220 |
|
STCB | Information on status: application discontinuation |
Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION |